The present invention relates to a process for producing 3,3-bis-(4-dimethylaminophenyl)-6-dimethylaminophthalide(crystalviolet lactone, hereinafter referred to as CVL), and more in detail, the present invention relates to (1) a process for producing CVL, which process comprises oxidizing 2-[4,4'-bis-(dimethylamino)-benzhydryl]-5-dimethylaminobenzoic acid in an aqueous mineral acid solution of pH of from 2.0 to 4.0 in the presence of at least one kind of catalyst selected from the group consisting of compounds of iron, copper, cobalt, nickel, chromium, vanadium and manganese by using air, oxygen or a gas containing oxygen, and (2) a process for producing CVL, which process comprises slowly adding tetramethyl-4,4'-diaminobenzhydrol into an aqueous mineral acid solution of pH of from 1.5 to 3.0 containing m-dimethyl-aminobenzoic acid, thereby forming 2-[4,4'-bis-(dimethylamino)-benzhydryl]-5-dimethylaminobenzoic acid, adding a catalyst comprising a compound of transition metal to the reaction mixture and oxidizing the thus formed 2-[4,4'-bis-(dimethylamino)-benzhydryl]-5-dimethylaminobenzoic acid in the resultant reaction mixture by using air, oxygen or a gas containing oxygen.
Although CVL itself is colourless or nearly colourless, it has a property of rapidly developing blue-violet colour in the case of bringing CVL into close contact with an electron-accepting substance, for instance, an organic acid, acid clay, phenol-formalin resin, a metal salt of an aromatic carboxylic acid and bisphenol A, and CVL is most broadly used as the pigment for recording materials such as pressure-sensitive recording paper sheets, heat-sensitive recording paper sheets, etc.
As the process for producing CVL, although many processes wherein 2-[4,4'-bis-(dimethylamino)-benzhydryl]-5-dimethylaminobenzoic acid(hereinafter referred to as LC) is oxidized into CVL have been known, it is difficult to obtain CVL of a high quality in a high yield because of the complexity of the steps of production and the large amount of the by-products due to decomposition.
For instance, in the process of oxidizing LC in an aqueous mineral acid solution with lead peroxide or potassium permanganate (refer to U.S. Pat. No. 2,417,897), in the process of oxidizing LC in an organic solvent such as glacial acetic acid, chloroform, etc. with oxygen in the presence of a metal complex [refer to Japanese Patent Application Laid-Open (KOKAI) No. 48-25730 (1973) (U.S. Pat. No. 3,828,071)] and also in the process of oxidizing LC in a liquid mixture of a nonaqueous solvent of hydrocarbon series and water with hydrogen peroxide in the presence of an acid catalyst [refer to Japanese Patent Application Laid-Open (KOKAI) No. 52-78867 (1977)], a large amount of tarry by-products is formed, thereby remarkably reducing the yield and the quality of CVL, and such a process requires the complex step such as the recovery of the organic solvent. Furthermore, in the process of oxidizing LC with hydrogen peroxide in an aqueous solution or a water soluble organic solvent in the presence of an alkali [refer to Japanese Patent Application Laid-Open (KOKAI) No. 52-31384 (1977)] and also in the process of oxidizing LC with hydrogen peroxide, oxygen, or air in an aqueous alkaline solution in the presence of a catalyst comprising a compound of cobalt or copper [refer to Japanese Patent Publication No. 59-19548 (1984) (U.S. Pat. No. 4,271,075)], a large amount of the unreacted substance is contained in the reaction product, thereby forming lumpy materials. Namely, the reaction hardly proceeds and the yield and the quality of CVL are very poor.
Besides, as the process for synthesizing LC as the intermediate for producing CVL, a process of reacting m-dimethylaminobenzoic acid(hereinafter referred to as DABA) with tetramethyl-4,4'-diaminobenzhydrol(hereinafter referred to as MH) in an aqueous solution of sulfuric acid (refer to U.S. Pat. No. 3,842,103) and a process of the reaction by dropping an aqueous sulfuric acid solution of MH into an aqueous sulfuric acid solution of DABA(refer to German Patent No. 2156648) have been known, however, in each of the two processes, the amount of the by-products due to decomposition is large and the yield and the quality of LC are extremely low.
It has been known that the yield and the quality of CVL synthesized by oxidation of LC are generally influenced by the quality of LC and accordingly, the isolation and purification of LC are carried out ordinarily before subjecting LC to oxidation. For instance, although there is a method of treating LC of a mixture with an aromatic hydrocarbon or a water-insoluble alkane [refer to Japanese Patent Application Laid-Open (KOKAI) No. 53-115740 (1978)(Canadian Patent 1087202)], there are the defects that the recovery of the solvent is troublesome and the loss of LC is large in the treatment of recovery thereof.
Moreover, the process for producing CVL consists essentially of the first step of reacting DABA with MH to form LC and the second step of producing CVL by oxidizing the thus obtained LC. According to the conventional process, LC obtained in the first step is generally separated and purified and then the separated and purified LC is used as the starting material in the second step. However, since the loss of LC accompanying the isolation and purification thereof is large, a method is also considered wherein the reaction mixture obtained in the first step is used as the starting material in the second step without separating and purifying, and the reaction of the second step is continuously carried out with the first step.
However, in such a method of continuously carrying out the reaction of the first step and the reaction of the second step, not only the remaining raw material, the decomposition products of the raw material, the by-products of reaction, etc. of the first step badly influence the yield of CVL in the second step but also, according to the conditions in the second step, the operations such as the separation of the tarry by-products and the recovery of the solvent accompanying the purification of the final objective material (CVL) uselessly complexed.
Particularly, in the technique of the first step, a large amount of by-products other than LC is formed, and in consideration of only the above-mentioned point, the process of continuously carrying out the reaction of the first step and the reaction of the second step has been inadequate.
As a result of the present inventors' earnest studies for solving the defects of the conventional process for synthesizing CVL, it has been found by the present inventors that (1) LC of an extremely high quality can be obtained in a high yield by adding MH into an aqueous mineral acid solution of pH of from 1.5 to 3.0 containing DABA, and CVL of a high quality can be obtained in a high yield in a short time by oxidizing LC as the intermediate of the production of CVL, in an aqueous mineral acid solution of pH of from 2.0 to 4.0 in the presence of a catalyst comprising a compound of a transition metal selected from the group consisting of iron, copper, cobalt, nickel, chromium, vanadium and manganese by using air, oxygen or a gas containing oxygen or (2) CVL can be obtained in a continuous process from DABA and MH by slowly adding MH into an aqueous mineral acid solution of pH of from 1.5 to 3.0 containing DABA, thereby forming LC, then adding the catalyst comprising the compound of the transition metal to the reaction mixture and oxidizing the thus formed LC in the resultant reaction mixture with air, oxygen or a gas containing oxygen, and on the basis of the